The present invention relates generally to an additional information superimposing method, an additional information detecting method, an additional information superimposing apparatus, and an additional information detecting apparatus for superimposing additional information such as duplication control information and copyright information for example onto an image signal and detecting the superimposed additional information from this image signal as required.
With the recent proliferation of digital content such as the Internet, CDs (Compact Discs), and DVDs (Digital Versatile Discs), copyright violations of digital content due to its unauthorized duplication have been problems. To deal with these problems, several schemes have been proposed in which additional information for duplication control is superimposed on digital content by means of electronic watermarking for example to prevent unauthorized duplication and limit the use of the digital content thus duplicated.
In electronic watermarking, information is embedded as noise into portions of an image or audio signal which are not essential in human recognition, or portions which are not redundant to music and video. The information thus embedded in an image or audio signal is hardly removed therefrom. On the other hand, even after an image or audio signal embedded with electronic watermark is filtered or compressed, the embedded watermark can be detected from this signal.
A duplication control scheme based on electronic watermarking provides, depending upon the additional information to be embedded as watermark, the following four conditions to represent the duplication generations and duplication control states of video or audio signals embedded with watermark information superimposed:
(1) copy free;
(2) copy once;
(3) no more copy; and
(4) never copy.
(1) xe2x80x9cCopy freexe2x80x9d denotes that an audio or image signal concerned can be duplicated freely. (2) xe2x80x9cCopy oncexe2x80x9d denotes that an audio or image signal concerned can be duplicated only once. (3) xe2x80x9cNo more copyxe2x80x9d denotes that the duplication made under the condition (2) xe2x80x9cCopy oncexe2x80x9d is prohibited for further duplication. (4) xe2x80x9cNever copyxe2x80x9d denotes that an audio or image signal is prohibited at all.
Thus, electronic watermark information indicative of a duplication generation or a duplication control state is embedded in an image or audio signal. When this signal is copied by the user into another storage medium, the embedded watermark information in the signal is detected. According to the duplication generation and duplication control state included in the detected watermark information, the signal is controlled in recording or reproduction, thereby surely preventing the unauthorized duplication of content such as image and audio signals.
In superimposing multiple-bit additional information onto a digital image signal for example as electronic watermark information, each electronic watermark information corresponding to each bit of the additional information is superimposed in a predetermined superimposition area of each frame, for example, of the digital image signal. However, if such superimposition areas are arranged sequentially and fixedly along time axis, the additional information superimposed on the image signal as electronic watermark information would be easily falsified or otherwise tampered.
To be more specific, if it is clear which bit of the additional information is superimposed at which position of each frame of the image signal, the electronic watermark information may be easily falsified for unauthorized duplication.
Sometimes, in addition to the above-mentioned duplication control information, a digital image signal is superimposed with an APS (Analog Protection System) information for preventing the duplication of an analog image signal if this digital image signal is converted into it and additional data such as copyright information for example as electronic watermark information.
Thus, when plural pieces of additional information are superimposed as electronic watermark information onto an image signal, arrangement of superimposition areas fixedly along time axis also makes it easily known which additional information is superimposed in which location of the image signal. This would make it easy to falsify the duplication control information and APS information for the unauthorized duplication of image signals.
It is therefore an object of the present invention to provide an additional information superimposing apparatus for superimposing additional information onto an information signal, comprising: a particular-pattern generating means for generating a plurality of particular patterns corresponding to the additional information; a rotating means for rotating, in a predetermined order, a sequence in which the plurality of particular patterns are arranged and outputting the sequentially rotated particular patterns; a phase inverting means for inverting the phases of the plurality of particular patterns for every predetermined period and outputting the phase-inverted particular patterns; and a superimposing means for superimposing each of the sequentially rotated and phase-inverted particular patterns onto each of predetermined units of the information signal.